This invention relates to methods of installing frames for access pits and manholes, and more particularly frames for supporting multiple covers or gratings above such pits or manholes.
Where an access pit or manhole having a clear opening of relatively large area is to be provided with a multiple-cover arrangement capable of withstanding heavy loads, it is conventional practice to span the opening by means of one or more I-section steel beams (rolled steel joists) so as to divide the area to be covered into a number of smaller areas. Each of these smaller areas is then covered by a number of covers disposed side by side, each cover extending between two adjacent beams, or between a beam and the adjacent wall of the pit, and being supported at its ends by parallel frame members, at least one of which is supported on the upper surface of a beam. Where two covers are positioned symmetrically on either side of the centre line of a supporting beam, the beam carries a separate frame member for each cover, the two frame members being supported by the two upper flanges respectively of the beam. There is normally a gap between the two adjacent frame members which is filled with concrete in order to increase the rigidity of the structure.
However, where such covers are to be subjected to high loads, for example in docks, airports and general heavy traffic areas, the upper flanges on the beam may become deformed by excessive loading of the frames. This may result in the beams becoming eccentrically loaded leading possibly to failure of the beams.
It is an object of the invention to obviate these disadvantages by using an entirely novel installation method which ensures that eccentric loading of the beams does not occur under heavy loading conditions.